Armodafinil
This page is a reference summary of published evidence and regulatory documents. It is not a substitute for individual medical advice, and it is not a recommendation to take or avoid any medicine.
Medically reviewed by Dr. Sofia Lindqvist, · Last reviewed 11 August 2026
Armodafinil is the isolated R-enantiomer of modafinil, sold as Nuvigil and approved by the FDA in 2007.
Modafinil is a racemic mixture: equal parts of two mirror-image forms of the same molecule, designated R and S. Armodafinil is the R form alone. Same molecular formula, same molecular weight, different stereochemistry.
On this page
Why the difference matters
150 mg
standard daily dose
~13 h
terminal half-life
+33–40%
exposure per mg vs modafinil
2007
year of FDA approval
The two enantiomers clear at different rates. The R form has a half-life three to four times longer than the S form.
Removing the S form therefore changes the shape of the concentration curve without changing the terminal half-life. Modafinil declines biphasically, with an early rapid drop as the S isomer clears. Armodafinil declines in a single smooth phase, because there is no S isomer to lose.
peak
zero
0h
4h
8h
12h
16h
20h
24h
Armodafinil 150 mg — one smooth decline
Modafinil 200 mg — biphasic
Illustrative shape of the two curves after a standard morning dose. Note that both reach the same terminal slope; the difference is in the middle of the day.
Armodafinil is commonly described as “lasting longer” than modafinil. That is imprecise. The terminal half-lives are about the same, near thirteen hours. What differs is that armodafinil holds higher concentrations later in the dosing interval.
Approved uses
The same three indications as modafinil: narcolepsy, excessive sleepiness associated with obstructive sleep apnea on adequate primary treatment, and shift work disorder.
Dosing
The standard dose is 150 mg once daily, against 200 mg for modafinil. The lower number reflects greater systemic exposure per milligram — roughly 33 to 40 percent higher.
| Modafinil | Armodafinil | |
|---|---|---|
| Standard dose | 200 mg once daily | 150 mg once daily |
| Isomers present | R and S | R only |
| Decline pattern | Biphasic | Monophasic |
| Terminal half-life | ~15 hours | ~13 hours |
| Interchangeable? | No — not bioequivalent | No — not bioequivalent |
Because the two did not meet FDA bioequivalence criteria, they are not interchangeable at equal milligram doses. Any switch involves a dose change made by a prescriber.
Safety
The adverse event profile and the drug interactions are broadly the same as modafinil, which follows from their being the same molecule. That includes the serious dermatological reactions, the psychiatric warnings, the cardiovascular cautions, and the CYP3A4 interaction with hormonal contraceptives.
Postmarketing data for armodafinil has included fatalities associated with drug hypersensitivity, including DRESS.
Pregnancy
The same concerns apply as for modafinil. Where regulators in Canada and the United Kingdom addressed only modafinil in their pregnancy communications, that was because armodafinil is not marketed there — not because it was judged safer.
Availability and names
Armodafinil is not marketed in Canada, the United Kingdom, or various other countries. Where it is unavailable, modafinil is the equivalent option.
It is sold in some markets as Waklert and Artvigil: the same molecule from different manufacturers.
Is armodafinil stronger than modafinil?
Per milligram, yes: systemic exposure is roughly 33 to 40 percent higher, which is why the standard dose is 150 mg rather than 200 mg. That is a difference in exposure, not a difference in kind.
Does armodafinil last longer?
Not in terms of terminal half-life, which is about thirteen hours for both. Armodafinil holds higher concentrations later in the day because there is no rapidly cleared S-isomer, which is what people usually mean by ‘lasts longer’.
Can I swap 200 mg modafinil for 150 mg armodafinil?
Not on your own. The two did not meet FDA bioequivalence criteria and are not interchangeable at equal milligram doses. Any switch involves a dose decision made by a prescriber.